From: Paul Mackerras <paulus@samba.org>
Date: Wed, 23 Oct 2013 08:40:02 +0000 (+0100)
Subject: powerpc: Don't corrupt user registers on 32-bit
X-Git-Tag: omap-for-v3.13/fixes-for-merge-window-take2~19^2~45^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=955c1cab809edfb5429603c68493363074ac20cf;p=pandora-kernel.git

powerpc: Don't corrupt user registers on 32-bit

Commit de79f7b9f6 ("powerpc: Put FP/VSX and VR state into structures")
modified load_up_fpu() and load_up_altivec() in such a way that they
now use r7 and r8.  Unfortunately, the callers of these functions on
32-bit machines then return to userspace via fast_exception_return,
which doesn't restore all of the volatile GPRs, but only r1, r3 -- r6
and r9 -- r12.  This was causing userspace segfaults and other
userspace misbehaviour on 32-bit machines.

This fixes the problem by changing the register usage of load_up_fpu()
and load_up_altivec() to avoid using r7 and r8 and instead use r6 and
r10.  This also adds comments to those functions saying which registers
may be used.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Tested-by: Scott Wood <scottwood@freescale.com> (on e500mc, so no altivec)
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

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